Gum bases, for use in chewing gum, are typically manufactured using antioxidants. The antioxidants must be added at sufficient levels into the gum base to provide stability of a) the gum base ingredients, during manufacture of the gum base; b) the gum base and other chewing gum ingredients, during manufacture of the chewing gum; and c) the finished chewing gum product, during shelf storage.
The most severe conditions requiring antioxidant generally occur during manufacture of the gum base, as a result of the relatively high shear, high temperature and long mixing times required to disperse the elastomer, filler, and other gum base ingredients. For instance, a two hour total mixing time at 280.degree. F. is common for a conventional batch process used to make gum base. Even though the antioxidant is often added late, along with fats and oils, a half hour or more is often required to incorporate the stabilized fats and oils into the base. During this time, much of the antioxidant initially added is often lost due to degradation and volatilization from the heat. This loss may exceed 40% of the initial antioxidant.
Compared to the gum base manufacturing process, the preparation of chewing gum product from gum base and other chewing gum ingredients is much more gentle. Any loss of antioxidant during the later manufacture of chewing gum is generally much less significant, or even negligible, compared to the loss of antioxidant during the initial manufacture of chewing gum base.
The synthetic antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are effective stabilizers for finished chewing gum products at levels of about 10-100 parts per million (ppm). Because the gum base generally constitutes about 10-50% by weight of the chewing gum product, these antioxidants are added at higher concentrations during manufacture of the gum base. During the mixing of the gum base ingredients, these antioxidants partially volatilize or degrade into complex furans, biphenyl compounds, and other unwanted chemicals. The initial addition of antioxidant into the gum base must be sufficiently high to permit these losses as well as the dilution of antioxidant occurring when the gum base is combined with other chewing gum ingredients.
Other synthetic antioxidants, and natural antioxidants, volatilize or degrade to some extent during gum base manufacture. These other antioxidants include, for example, tert-butyl hydroquinone (TBHQ) and tocopherols. In order to minimize the degradation of antioxidant, and reduce the amount of unwanted chemical by-products, there is a demand for a process which efficiently combines the gum base ingredients using less severe conditions.